Method of making a composite tank

ABSTRACT

A composite tank for containing liquid oxygen and the method of making the same wherein a water-soluble mandrel having the desired tank configuration and a cylindrical A method of making a composite tank for containing liquid oxygen configuration of the mandrel and an outer boss conforming to the configuration of the inner boss, the bosses each having a tubular portion for receiving the protuberance on the mandrel and a spherical portion. The mandrel and the bosses are first coated with a nickel coating. The mandrel is then wrapped with graphite fibers wetted with an epoxy resin and this resin is cured. A layer of insulating foam is then applied to the tank and cured. The insulating foam is machined to a desired configuration and a layer of aramid fibers wetted with a second epoxy resin is wrapped around the tank. The second resin is cured and the water soluble mandrel is washed from inside the tank.

This application is a division of application Ser. No. 09/218,652, filedDec. 22, 1998, pending.

ORIGIN OF THE INVENTION

This invention was made by an employee of the United States Governmentand may be manufactured or used by or for the Government forGovernmental purposes without the payment of royalties thereon ortherefor.

BACKGROUND OF INVENTION

1. Field of the Invention

This invention relates to composite tanks.

2. Prior Art

It is known to make tanks from composite materials for various purposes.There has been considerable prior art in general for double-walled tanksfor puncture resistant underground storage of environmentally hazardouschemicals, for example. There is a need for tanks and pressure vesselsfor the containment of fuels for aerospace and military applications.The new launch vehicles for NASA and DOD require extremely light weighthardware that is compatible with the containment of cryogenic liquidfuels and oxidizers. Long term deep space missions have even morecritical and stringent storage requirements.

SUMMARY OF THE INVENTION

A method of making a composite tank for containing liquid oxygen whereina water-soluble mandrel having the desired tank configuration and acylindrical protuberance on at least one end is fitted with an innerboss conforming to the configuration of the mandrel and an outer bossconforming to the configuration of the inner boss, the bosses eachhaving a tubular portion for receiving the protuberance on the mandreland a spherical portion. The mandrel and the bosses are first coatedwith a nickel coating. The mandrel is then wrapped with graphite fiberswetted with an epoxy resin and this resin is cured. A layer ofinsulating foam is the applied to the tank and cured. The insulatingfoam is machined to a desired configuration and a layer of aramid fiberswetted with a second epoxy resin is wrapped around the tank. The secondresin is cured and the water soluble mandrel is washed from inside thetank.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of the mandrel on which the composite tank is tobe formed showing the inner and outer bosses at the ends of the mandrel.

FIG. 2 is a greatly enlarged fragmentary view showing the structuremaking up the composite tank.

DETAILED DESCRIPTION OF THE INVENTION

Referring now in detail to the drawings there is shown in FIG. 1 amandrel 11 having a desired tank configuration and a pair of cylindricalprotuberances 12 extending from each end. Positioned on eachprotuberance 12 is an inner boss 15 which is made up of a tubularportion 16 and a spherical portion 17. The tubular portion 16 snuglyfits the protuberance 12 while the spherical portion conforms to theconfiguration of the end of the mandrel 11. The inner bosses 15 are madeof a nickel plated metal, preferably aluminum.

Positioned on the inner bosses 15 are a pair of outer bosses 21 made upof graphite fibers embedded in a cured epoxy resin matrix. The outerbosses have tubular portions 22 secured to spherical portions 23. Thetubular portions fit snugly on the tubular portions 16 of the innerbosses 15 and the spherical portions 23 conform to the outer surfaces ofthe spherical portions 17 of the inner bosses 15.

After the inner and outer bosses 15 and 21, respectively, are in placethe mandrel and the bosses are coated with a nickel coating 24. Thiscoating shown in FIG. 2, may be applied by an electroforming process orby a vacuum plasma spraying process. The diameters of the sphericalportions 17 of the inner bosses 15 are greater than the diameters of thespherical portions 23 of the outer bosses. This is to insure that whenthe nickel coating is applied it will cover the exposed portion of thespherical portions 17 of the inner bosses 15 to completely seal thegraphite outer bosses 21 in a nickel coating.

After the nickel coating has been applied to the mandrel and the bosses,the mandrel 11 is wrapped with a tow of graphite fibers wetted with anepoxy resin and the epoxy resin is cured to form a first layer 27 ofgraphite fibers embedded in a cured resin matrix. A layer 32 of aninsulating foam is then sprayed onto the tank and, after curing, ismachined to the desired configuration. Preferably, the foam is apolyurethane foam.

A tow of aramid fibers wetted with an epoxy resin in then wrapped overthe insulating foam and the resin is then cured to provide a layer 33 ofaramid fibers embedded in a cured epoxy resin matrix. If desired, a thincoating 34 of rubber may be sprayed over the aramid fiber layer. Thewater-soluble mandrel 11 is then washed out of the tank to leave a verystrong tank. The bosses at each end provide for access to the interiorof the tank.

What is claimed is:
 1. A method of making a composite tank for liquidoxygen, comprising a. providing a mandrel having a desired tankconfiguration and having a cylindrical protuberance on at least one endof said mandrel; b. placing on said end of said mandrel a nickel platedinner boss having a configuration conforming to the said end of themandrel; c. placing on the inner boss an outer boss having aconfiguration conforming to the configuration of the inner boss, thesecond boss being made up of graphite fibers embedded in a cured epoxyresin matrix; d. coating the mandrel and the bosses with nickel; e.wrapping the mandrel with a tow of graphite fibers wetted with a firstepoxy resin; f. curing the first epoxy resin to form a layer of graphitefibers in an epoxy resin; g. applying a layer of insulation foam to thelayer of graphite fibers; h. curing the layer of foam; i. machining thefoam to a desired thickness; j. wrapping the foam layer with a tow ofaramid fibers wetted with a second epoxy resin; and k. curing the secondepoxy.
 2. The method of claim 1 wherein the inner boss is made of nickelplated aluminum.
 3. The method of claim 2 wherein a coating of rubber isapplied to the layer of aramid fibers.